type Server interface {
	// From returns proxy source address in "scheme://host:port" format.
	From() string
	// To returns proxy destination address in "scheme://host:port" format.
	To() string

	// Ready returns when proxy is ready to serve.
	Ready() <-chan struct{}
	// Done returns when proxy has been closed.
	Done() <-chan struct{}
	// Error sends errors while serving proxy.
	Error() <-chan error
	// Close closes listener and transport.
	Close() error

	// PauseAccept stops accepting new connections.
	PauseAccept()
	// UnpauseAccept removes pause operation on accepting new connections.
	UnpauseAccept()

	// DelayAccept adds latency ± random variable to accepting
	// new incoming connections.
	DelayAccept(latency, rv time.Duration)
	// UndelayAccept removes sending latencies.
	UndelayAccept()
	// LatencyAccept returns current latency on accepting
	// new incoming connections.
	LatencyAccept() time.Duration

	// DelayTx adds latency ± random variable for "outgoing" traffic
	// in "sending" layer.
	DelayTx(latency, rv time.Duration)
	// UndelayTx removes sending latencies.
	UndelayTx()
	// LatencyTx returns current send latency.
	LatencyTx() time.Duration

	// DelayRx adds latency ± random variable for "incoming" traffic
	// in "receiving" layer.
	DelayRx(latency, rv time.Duration)
	// UndelayRx removes "receiving" latencies.
	UndelayRx()
	// LatencyRx returns current receive latency.
	LatencyRx() time.Duration

	// ModifyTx alters/corrupts/drops "outgoing" packets from the listener
	// with the given edit function.
	ModifyTx(f func(data []byte) []byte)
	// UnmodifyTx removes modify operation on "forwarding".
	UnmodifyTx()

	// ModifyRx alters/corrupts/drops "incoming" packets to client
	// with the given edit function.
	ModifyRx(f func(data []byte) []byte)
	// UnmodifyRx removes modify operation on "receiving".
	UnmodifyRx()

	// BlackholeTx drops all "outgoing" packets before "forwarding".
	// "BlackholeTx" operation is a wrapper around "ModifyTx" with
	// a function that returns empty bytes.
	BlackholeTx()
	// UnblackholeTx removes blackhole operation on "sending".
	UnblackholeTx()

	// BlackholeRx drops all "incoming" packets to client.
	// "BlackholeRx" operation is a wrapper around "ModifyRx" with
	// a function that returns empty bytes.
	BlackholeRx()
	// UnblackholeRx removes blackhole operation on "receiving".
	UnblackholeRx()

	// PauseTx stops "forwarding" packets; "outgoing" traffic blocks.
	PauseTx()
	// UnpauseTx removes "forwarding" pause operation.
	UnpauseTx()

	// PauseRx stops "receiving" packets; "incoming" traffic blocks.
	PauseRx()
	// UnpauseRx removes "receiving" pause operation.
	UnpauseRx()

	// ResetListener closes and restarts listener.
	ResetListener() error
}

type ServerConfig struct {
	Logger        *zap.Logger
	From          url.URL
	To            url.URL
	TLSInfo       transport.TLSInfo
	DialTimeout   time.Duration
	BufferSize    int
	RetryInterval time.Duration
}